They have their own audience share, not all can afford paying for prime channels. FTA channels can never eat into viewership of pay channels, but yes there r people like me who watch both. Pay channels are not improving upon content or connecting with audience to know their likings. Also OTT and cheap internet is driving audience away which is again result of changing or advancement of technology.
Take case of hindi movies, english movies or shows, music or even infotainment or news... All these r available for free these days alingwith almost free internet which is bound to reduce TV audience for channels operating in these genres. Only older generation or those still not having access to OTT r continuing TV viewing.
Lastly even in US , UK etc. FTA channels remain highly popular that too in DTT broadcast.